The present invention relates to a light-weight building material which can be formed into a wall board and the like shaped article or used as a blow-on insulating material in buildings as well as a method for manufacturing the same. More particularly, the invention relates to a light-weight building material of the above mentioned type manufactured very inexpensively from scrapped paper and aluminum hydroxide-containing sludge.
Needless to say, there are currently on use in the building industry a great variety of building materials depending on the requirements for the particular building and locality. The requirements for the building materials are so diversified that a material suitable in a building is not always useful in another. Several characteristics are, however, almost always important in any types of building materials among which, for example, are mechanical strength, nonflammability or flame retardancy and heat and sound insulation as well as inexpensiveness.
In relation to the inexpensiveness of the building materials, there may be obtained two-way advantages simultaneously if an industrial waste can be processed or fabricated into building materials having satisfactory characteristics in the solution of the problem caused by the burdensome waste material such as the environmental pollution and the commercial benefit obtained with the building materials produced therefrom with outstanding inexpensiveness.
Accordingly there have been made various attempts to utilize useless industrial waste materials for the production of building materials. Unfortunately there are known very few examples of success in which excellent building materials suitable for practical use are manufactured from an otherwise useless or rather harmful industrial waste as the main starting material.
Turning now to give an overview of the industries involving a serious problem of waste disposal to avoid environmental pollution, the aluminum fabrication works are typically notorious due to the difficulties in the waste disposal. As is well known, aluminum articles in recent years are used rarely as shaped by extrusion, casting or other shaping means with the metallic aluminum surface exposed but almost always used after surface finishing.
The method of surface finishing most widely undertaken in the aluminum industry is, of course, the surface anodization in which the surface of the aluminum article is electrolytically oxidized in an acidic electrolyte bath to be covered with a thin but dense layer of aluminum oxide and imparted with increased chemical and physical stability as well as beauty. A problem in the anodization treatment of aluminum articles is that a considerable amount of aluminum metal unavoidably is dissolved in the electrolyte bath and the thus dissolved aluminum finally precipitates in the form of amorphous aluminum hydroxide forming a gel-like sludge when the electrolyte solution is neutralized for sewage disposal.
The gel-like sludge usually contains large volumes, e.g. 70 to 90% by weight, of water but is hardly filtrable so that drying up of such an aluminum hydroxide sludge is practically impossible. Therefore, the only way in the art for the disposal of the aluminum hydroxide sludge is to discard it in a reclaimed land or in the ocean in the gel-like form as such.
Such a method of waste disposal is, of course, not quite acceptable even setting aside the problem of the large cost for the transportation of such a watery waste material to the reclaimed land or off to the ocean. For example, a reclaimed land filled with such a gel-like sludge is naturally weak in the yield strength of the ground resulting in a decreased utilizability of the land. Discarding of the sludge in the ocean is also not free from regulations to prevent pollution of water. Thus the waste disposal of the gel-like aluminum hydroxide sludge has been the most troublesome problem in the industry of aluminum fabrication.